1. Field of the Invention Received
The present invention relates to a novel process for preparing soluble phthalocyanines by microwave irradiation in the absence of any organic solvents and represented by the general formula shown in FIG. 1 wherein R is an alkyl group such as t-butyl or an alkoxy group like pentoxy, and Mt is a metal or non-metal, like Co, Ni, Cu, Mg, Al, Pd, Sn, Tb, Lu, Ce, La, Zn, or H.
2. Description of the Related Prior Art
Phthalocyanines exhibit extremely good stability and photoelectric properties due to its unique chemical structure, and hence have been used widely. They are currently the largest consumed dyes and/or pigments in the world, and play a major role in the application for the high technology industry.
Phthalocyanines can be made into a film that in turn can be fabricated into an element by means of a variety of methods. Among those methods, the spin-coating has the lowest cost(1-2). Films made from phthalocyanines have been applied over various fields such as photo-recording materials(3-4), gas sensors(5), electrochromic elements(6), non-linear optics (NLO)(7) and photocells(8).
The structural formula of phthalocyanines is given in FIG. 1, wherein R represents alkyl, t-butyl, or an alkoxy group like pentoxy, and Mt represents a central material of metal, like Co, Ni, Cu, Mg, Al, Pd, Sn, Tb, Ce, La, Zn, Lu or a metal-free material like H atom.
Microwave was developed from the radar during the Second World War. At that time, it was discovered that microwaves emitted from the radar were capable of drying large ceramic objects. The application of microwaves for the household electric commodities had been, however, since 1970. Nevertheless, in recent years, many studies have been devoted to exploring the feasibility of the application of microwaves on chemical reactions.
Microwave is an energy in the form of an electromagnetic wave. It is a non-ionization radiation that can induce the migration of electron and the rotation of dipole moment, and hence cause the motion of a molecule. Microwave heating is different from conventional heating method mostly in its mode of energy delivery. Traditional heating method delivers heat energy by conducting through a container containing the solution, and homogeneously distributes the heat to the solution and hence raising the temperature thereof. On the contrary, microwave heating delivers heat by radiation, and therefore, can heat reactants directly and accordingly promoting its efficiency.
Synthesis of phthalocyanine by microwave irradiation was first proposed by Ahmad Shaabani(12) in 1998 using a phthalic anhydride lacking a side group as the starting material. This method had, however, a disadvantage in that the phthalocyanine synthesized had a poor solubility. It is insoluble in almost every solvent other than concentrated sulfuric acid. In 1999, Cezar Ungurenasu(13) proposed a process for preparing phthalocyanine by microwave irradiation with phthalonitrile or diiminoisoindoline as the starting material. The product thus prepared had a defined solubility, however, it was disadvantageous in that the solvent must be involved in the reaction, i.e., it was not a dry preparation, and hence contained high production cost. Further, it differed from the scope claimed by the present invention.
The traditional syntheses of phthalocyanine, no matter what starting material is used, required a relatively long reaction time and a considerable high energy to provide sufficient kinetic energy to overcome the reaction kinetic barrier and hence, promote the collision probability and energy of molecules, which results in low efficiency. Accordingly, the object of the present invention is to provide a novel process for preparing phthalocyanine by microwave irradiation that can eliminate the above-described disadvantage associated with the traditional process. Consequently, it is possible to shorten the reaction time, and produce soluble phthalocyanines that can be used to fabricate elements by avoiding an expensive vacuum sputtering method, and thus, increasing its industrial practicability.